The present invention relates to electrical safety devices, and more particularly to a device for monitoring ground pick-up and the ground and polarity integrity of a polarized electrical service receptacle. In one embodiment of the present invention further means are included to temporarily correct a reversal of polarity without requiring the receptacle to be rewired.
The safety hazards associated with improperly grounded or incorrectly polarized electrical service outlets are well appreciated by those skilled in the art as constituting significantly dangerous conditions. As a result of these conditions, cases of severe electrical shock, at times sufficient to create a fatal condition, occur on a more than infrequent basis. Complicating the safety aspect of these conditions is the fact that they generally occur without any noticeable loss of electrical service and therefore do not receive immediate corrective attention.
For example, for safety purposes an uninsulated electrical tool will often have its chassis grounded through the ground service terminal of a wall outlet. Since the tool is powered by means of the hot and neutral service terminals of the outlets, a poor ground connection, although presenting a safety hazard, will not result in any loss of power to the tool. Thus, the user of the tool will continue about his work unsuspecting of the safety hazard. However, once a circuit is completed from the hot chassis through the user to ground (perhaps by the user coming into conductive contact with a grounded house pipe), a potentially dangerous shock hazard is created. Of course, a similar hazard will be presented in the case where the ground prong of the tool plug has, for some reason, been removed thereby preventing the grounding of the chassis even though the service receptacle ground may be intact.
Similarly, the neutral service terminal is frequently used for safety purposes, to ground the chassis of a tool. If the polarity of the service receptacle is reversed, instead of grounding the chassis the high potential at the hot service terminal will be applied directly thereto. It will be appreciated that such a reversal of polarity creates the possibility of shock in a manner similar to that created by an improperly grounded service terminal. And, as discussed with respect to an improper ground condition, the reversal of polarity will not be manifested by any improper operation of the tool since the receptacle is supplying an A.C. voltage.
Not infrequently the situation arises where the service receptacle is properly grounded but the polarity thereof is reversed. Although this condition should eventually be corrected by rewiring the outlet, it is frequently desirous to be able to temporarily use the outlet prior thereto. But, in order to do so, preliminary precautions must be taken to insure that the outlet can be safely used.
The prior art discloses numerous devices for monitoring the ground and polarity integrity of a service receptacle. Furthermore, the prior art also discloses apparatus for correcting the polarity of an incorrectly polarized receptacle. However, these prior art devices exhibit certain undesirable operating characteristics and, in addition, are frequently quite complicated to operate and do not provide a simple means by which an electrical novice may be assured of a safe wall receptacle and an opportunity to temporarily and safely correct an incorrectly polarized condition.
For example, U.S. Pat. No. 3,317,825 discloses a three lamp unit for testing the wired condition of a three-wire grounded type electrical receptacle. Although this type of device may be adequate for use by an experienced electrician, the complexity associated with correlating lamp indications renders its use undesirable in connection with a novice. And, in addition to exhibiting a complex design presenting the possibility of frequent malfunction, the device is incapable of correcting an incorrectly polarized receptacle.
U.S. Pat. No. 3,733,576 discloses a reversible safety ground plug which may be utilized to correct the polarity of an incorrectly polarized receptacle. However, in addition to necessitating the use of two retractable ground contacts, this device inherently presents a serious safety hazard. That is, although the device is adapted to provide an indication in the case of polarity reversal, this indication will be entirely masked by a bad ground connection. Therefore, even if a dangerous polarity reversal is present, no indication thereof will be provided if, simultaneously therewith, a poor ground connection exists. Under these conditions, the unsuspecting user will be lulled into a false and hazardous sense of security. Furthermore, the device disclosed in this patent is operable only in connection with a three terminal outlet which significantly minimizes its overall adaptability.